In view of the recent global environmental problems, the issues on development and dissemination of clean energy are being addressed globally. Among the clean energy sources, a fuel cell is receiving attention in recent years because of a low-emission and highly-efficient source. A fuel cell electrochemically oxidizes a fuel such as hydrogen and methanol by use of oxygen or air, and converts chemical energy of the fuel into electrical energy to be extracted. There are various types of fuel cells such as an alkaline type, a phosphate type, a molten carbonate type, a solid electrolyte type and a polymer electrolyte type, according to the type of electrolyte provided therein. Among these fuel cells, a polymer electrolyte fuel cell is highly expected to serve as a power source for a vehicle and household use because the polymer electrolyte fuel cell is operable in low temperature, is easy to handle, and has high power density.
In order to put a polymer electrolyte fuel cell into practical use particularly in a fuel cell for a vehicle, a reduction in size and high output power have been required. Therefore, it is necessary to reduce the thickness of an electrolyte and the volume of the fuel cell itself, as well as to decrease the internal resistance of the fuel cell. For this reason, developments of a hydrocarbon electrolyte membrane are being promoted, in addition to a conventional fluorine electrolyte membrane. As compared with a fluorine electrolyte membrane, a hydrocarbon electrolyte membrane has the advantages of manufacturing with inexpensive raw materials and simple steps, and being highly selective for materials. However, hydrocarbon electrolyte membranes developed in recent years are generally made from super engineering plastic having high resistance to heat and high rigidity as a base material. Thus, the hydrocarbon electrolyte membranes have high rigidity but have little flexibility and substantially low toughness. In addition, there is a problem of release of a sulfonic acid group under a high temperature condition. Therefore, the resolution of these problems is strongly desired.
In order to improve a mechanical strength, a polyurea electrolyte of which a side chain includes an ionizing functional group at a side chain, and a fuel cell using the polyurea electrolyte have been disclosed in recent years (for example, refer to Patent Literature 1 and Patent Literature 2). In addition, a proton conductive composite membrane has been proposed, in which a porous membrane in polyurea resin is filled with an acrylamide electrolyte (for example, refer to Patent Literature 3).